Winter light conditions profitable for aquaculture: research

Wild-captured Arctic charr farmed at land-based aquaculture facilities grow better if light conditions are adapted to suit winter, new research on environmentally-friendly aquaculture shows.

It is normal practice to provide farmed fish continual light so they grow as rapidly as possible. However, wild-captured Arctic charr have adapted to living in arctic conditions with little access to food in winter.

As a result, scientists have tested if a period of darkness in winter can further improve growth of Arctic charr. Senior Scientist Sten Siikavuopio says the tests have produced extremely good results.

"We have followed Arctic charr over a one-year period. After a period of winter light conditions, during which the fish had a break from the continual light, the Arctic charr grew 30 percent quicker than Arctic charr which received a continual supply of light."

Eating less - growing more

In late 2007 the Arctic charr experienced an eight-week "winter", during which they received eight hours of light each day followed by 16 hours of darkness. During this period, less feed was provided as the Arctic charr had a smaller appetite.

Land-based farming of Arctic charr functions in a manner that the amount of feed the fish receive depends on the amount they consume. Animal technicians check how much feed has disappeared and adjust the amount of feed the following day.

"This shows there are good reasons for Arctic charr farmers to make savings on both feed and electricity by introducing a short winter," says Siikavuopio.

Focus on environment

Environmental considerations play an extremely important role in this project. The Arctic charr originates from the lake Altevatn in Troms, where fish stocks out weight access to food.

It is advantageous to capture fish from this lake, as both the captured fish and those remaining gain better conditions. In addition, fish farmers require less time to produce Arctic charr ready for sale.

After the Arctic charr is captured in Altevatn, it is taken to VillmarksFisk's land-based facility in Bardu. VillmarksFisk is alone in farming wild-captured Arctic charr. The company is also a pioneer in Norway with respect to the utilisation of recirculating aquaculture systems (RAS).

The tests about winter light conditions are part of a larger research project on RAS headed by Bioforsk. The water pumped into the fish tanks goes through a so-called bio filter before returning to the tanks.

The bio filter contains bacteria which break down waste products and, of extreme importance, the water is purified from ammonia. The bacteria break the ammonia down to less damaging substances like nitrate, which enables the water to be reused. Before the water returns to the fish, oxygen and a little new water is added and redundant CO2 is removed so that the level becomes normal.

Recirculating cold water

For the first time water as cold as 8 ºC is being recirculated. It was previously believed that bacteria needed warmer water to break down waste products. However, this research project shows that they can also accomplish the task in cold water.

"The possibility of recirculating colder water provides better conditions for farming of Arctic charr," says Siikavuopio. "Given these results, it may be possible to farm other fish species."

The manager of OppdrettsTeknologi, Steinar Skybakmoen, says RAS is stable and functions well.

"We have not experienced a single case of excessive nitrite levels. The utilisation of recirculating aquaculture systems is a new way to run aquaculture in Norway," he says. "This technology makes it possible to farm fish virtually anywhere."

Inland land-based farming of fish has often involved problems with disposing of the large amounts of water required to provide good conditions for the fish. However, when the water is recirculated, only small amounts of water return to the ground, which the soil can cope with.

Waste becomes plant fertiliser

Yet another environmentally-friendly test has been conducted in connection with the wild-captured Arctic charr project with a use being found for fish excrement. This is separated as part of the recirculation process and has been used with good success as a plant fertiliser.

This is a collaboration project between Bioforsk, Fiskeriforskning, OppdrettsTeknologi and VillmarksFisk, and is being financed by the Research Council of Norway.

Senior Scientist Sten Siikavuopio is continuing to improve the use of winter light conditions for Arctic charr in a new joint project with VillmarksFisk and Kirkenes Charr. The new project will also study the effect of winter light conditions on sexual maturity and fish quality.

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Winter light conditions profitable for aquaculture: research